INTERMEDIATE CARBOHYDRATE METABOLISM 



13 



dioxide with pyruvic to oxalacetic acid has been proved by Evans 

 and by Wood and Werkman, we have only to assume that the car- 

 bonyl group of the latter is phosphorylated, forming a phospho-enol 

 oxalacetic acid; the phospho-enol group would then be equally 

 distributed between the alpha and beta position and the compound 

 again decarboxylated; so we obtain a phosphopyruvic acid, half of 

 which contains labeled carbon in the carboxyl group. Such a reaction 

 may well be coupled with oxidation of fumaric and malic acid to 



+ 



CH, 

 I 

 o<C=0 



I 

 COOH 



Pyruvic Acid 



C*OOH 



CHp 

 I 

 a C=0 + H3PO4 



COOH 

 Oxalacetic Acid 



+ H, 



-H; 



Malic 

 Acid 



COOH 

 I 

 CHp 



I 

 CHOH 



COOH 



•HpO 



+ HpO 



Fumaric 

 Acid 



COOH 

 I 

 CH 



CH 

 I 

 COOH 



I ^ 

 +H2 ' 



-H= 



Succinic 

 Acid 



COOH 

 I 



CHp 

 I 



CH3 

 I ' 

 COOH 



C*OOH 



CH 



II 

 ex C-O-HpPO, 

 I ^ 



COOH 



Phosphoenoloxalacetic Acid 



0*0 OH 



C-O-HpPO, 



II 

 a CH 

 J. 

 [C*00:H 



Phospho- 

 pyruvic 

 Acid 



C^OOH 

 I 

 C-O-HpPO, 



II 

 CH, 



(ctH.oOs), 

 Glycogen 



Figure 5. — Possible mode of uptake of carbon dioxide containing radioactive 

 carbon (C*) during synthesis of glycogen from lactic acid 



